Biological responses of small yellow croaker (Larimichthys polyactis) to multiple stressors: a case study in the Yellow Sea, China

Temporal changes in biological characteristics of small yellow croaker Larimichthys polyactis in the Yellow Sea were examined for the period of 1960-2008. The body size and age of small yellow croaker decreased substantially, in particular, average length of fish in 2008 was reduced by similar to 85% than those occurring in 1985, and at that time similar to 93% of the total catch was dominated by one-year-old individuals. Correspondingly, growth parameters also varied significantly over the years, i.e., k (growth coefficient) and t(0) (zero-length age) gradually increased from 0.26 and -0.58 year in 1960 to 0.56 and -0.25 year in 2008, respectively. Although, L infinity (body length) sharply decreased from 34.21 cm in 1960 to 24.06 cm in 2008, and t(r) (inflexion age) decreased from 3.78 year in 1960 to 1.61 year in 2008. There was a great increase both in natural mortality coefficient and fishing mortality coefficient. However, according to the gray correlation analysis, changes in the biological characteristics of small yellow croaker were induced by different stressors ranked as: fishing vessel power>feeding grade>sea surface temperature. This study suggests that the active fishery management measures for biological characters of fish populations should be considered.